The present invention concerns works such as motorway flyovers, underpasses, bridges, artificial tunnels, underground garages or carparks and other similar works that are constructed in the open air, that is, on a substantially level area which may be obtained following excavation below ground level before building the structure.
Various technical solutions are known for undertaking such works. In particular, prefabricated reinforced concrete articulated elements of, for example, the type described in European Patent EP-0 219 501, are widely used for this purpose.
Specifically, the prefabricated articulated elements are concrete elements, each being formed from several bodies that are joined together only by the reinforcement rods common to two adjoining bodies. These elements are produced in an extended, coplanar condition and, in this condition, they are more easily transported to the construction site. During installation, they are lifted using suitable slings in such a way that, due to the weight, the reinforcement rods bend at the predetermined articulation points between the various bodies such that each element automatically assumes its final configuration. Once installation is complete, the articulation points are fixed with cast sealing concrete and possible additional reinforcements incorporated in the joint between adjoining bodies. In these prefabricated articulated structures the continuity of the reinforcement in all of the tensioned parts in the finished structure, the exact arrangement of the reinforcements in use, and the simple and quick operations for installing the structure are guaranteed.
The prefabricated articulated elements are normally used in two different types of structure, in particular, closed frame box structures, and arch structures having three hinges.
Prefabricated elements intended for the construction of closed frame box structures each comprise five bodies separated by four articulations. An inverted U-shape structure is obtained upon lifting an element, which defines the two supporting uprights and the roof of the structure, in which the various bodies are disposed at approximately 45.degree. with respect to the adjacent bodies. The two uprights are then anchored in situ at the base by a single concrete casting which joins them together, and the final closed-frame box structure is obtained after sealing the articulations and the joints between the various adjoining prefabricated elements. This type of structure is optimally used for works having spans of approximately 3 to 6 m. In this way, the dimensions of the prefabricated articulated elements are still within the permitted shape limits for transportation by road, whereas prefabricated elements for closed box structures of the same section that are already in their final configuration would fall outside this shape limit.
For the construction of arch structures having three hinges, prefabricated elements are instead used that are joined in pairs to form a central hinge at the contact zone. Each of these prefabricated elements comprises three bodies separated by two hinges and, when installed, assumes the form of a rounded inverted L-shape in which each body forms an angle of substantially 45.degree. with the adjacent bodies. Each element of each pair rests via an associated hinge on an associated continuous foundation plinth cast in situ. The assembly of the two elements thus forms an arch having three hinges: two at the base, between each prefabricated element of the pair and each of the plinths, and a central hinge between the two prefabricated elements. These structures enable larger structures than the closed-frame box structure to be obtained, in practice, having spans of from 5-6 m to approximately 15 m, with the typical characteristic of three-hinge arch structures of being isostatic and therefore not subject to any stress state even if the plinths subside, in which case the entire structure is subject to deformation, but each individual isolated loop comprising a pair of adjoining elements is not as a whole subject to any stresses caused by the subsidence.
In general, in both of the known arrangements described above, the prefabricated elements form a completely stable assembly even before the sealing concrete castings. The assembly of the various prefabricated elements does not require any kind of temporary shoring means, such as underpinning, falsework and the like, following installation.
These known structures have the advantage that they can be formed extremely quickly while, at the same time, they are very reliable, well protected from ground corrosion, adapted to last a long time and to bear the weight of embankments of considerable height and maximum loads envisaged for road and railway works.
However, the main problem common to these known structures is that structures with a span exceeding approximately 15 m cannot be achieved while, at the same time, maintaining the dimensions of the individual prefabricated elements within the shape limits for road transport.